Vitamin D and Osteoporosis

There are powerful inherited contributions to osteoporosis with up to 75% of variance in bone phenotypes, such as bone mineral density, bone size, and geometry, attributable to genetic factors in healthy individuals. Allelic variation in the vitamin D receptor was the first nonstructural gene to be associated with osteoporosis. These data, in conjunction with the effects of the vitamin D system in bone homeostasis, suggested that this vitamin might have a strong role in osteoporosis treatment. This possibility is consistent with effects of the active vitamin D metabolites directly on osteoblasts to reduce osteoclast recruitment and increase their activity, while at the same time acting on the osteoclast pathway to increase osteoclast recruitment. In large-scale epidemiological data, serum 25-hydroxyvitamin D (25(OH)D) levels are associated with bone density in both men and women. However, there is mixed evidence on the effectiveness of vitamin D supplementation for the prevention of bone loss and minimal trauma fractures in postmenopausal women and older men. There is likely to be a benefit on primary fracture prevention for those with the highest background fracture risk, including those patients who have inadequate serum levels of 25(OH)D and institutionalized patients, but only when combined with calcium supplements. There is little evidence that vitamin D alone can prevent fractures, and no evidence that the combination of calcium and vitamin D, or either alone, can prevent fractures in patients with preexisting minimal trauma fractures.